MacViews: Implement Tab Dragging

ui/views/cocoa/views_nswindow_delegate.mm

Index: ui/views/cocoa/views_nswindow_delegate.mm
diff --git a/ui/views/cocoa/views_nswindow_delegate.mm b/ui/views/cocoa/views_nswindow_delegate.mm
index d8f1a8230ab989930baca03a532e22e620ec40be..3ee13514bae3da986a3e2b2cc33967b02d98c19f 100644
--- a/ui/views/cocoa/views_nswindow_delegate.mm
+++ b/ui/views/cocoa/views_nswindow_delegate.mm
@@ -79,6 +79,13 @@
   parent_->OnSizeChanged();
 }
 
+- (void)windowDidMove:(NSNotification*)notification {
+  // Note: windowDidMove: is sent only once at the end of a window drag. There
+  // is also windowWillMove: sent at the start, also once. Live updates are
+  // provided by BridgedNativeWidget only during RunMoveLoop().
+  parent_->OnPositionChanged();
+}
+
 - (void)windowDidBecomeKey:(NSNotification*)notification {
   parent_->OnWindowKeyStatusChangedTo(true);
 }